Heat 3 tablespoons olive oil in a large pot and sauté onion and garlic until golden, about 4 minutes. Stir in tomato paste, cumin, salt, pepper and chili powder or cayenne, and sauté for a couple more minutes.

Add stock, water, lentils and carrot. Bring to a simmer. Partially cover the pot and turn the heat to medium-low. Simmer until the lentils are soft, about 30 minutes. Taste and add additional salt, pepper, chili powder or cayenne if necessary.

Purée half of the soup (with an immersion blender or in a blender or food processor), then add back to the pot. The soup should be somewhat chunky. Reheat the soup gently.

When hot, stir in the lemon juice and cilantro. Serve the soup drizzled with olive oil and lightly dusted with chili powder